1. Field of the Invention
The present invention relates to a friction stir welder and a method for friction stir welding.
2. Description of the Related Art
Recently, a friction stir welding scheme has frequently been introduced to various cases, as a welding technique that reduces distortion or deformation of welded material pieces due to thermal influences caused by welding. For example, as disclosed in U.S. Pat. No. 6,051,325, a friction stir welding is performed in such a manner that a pair of works (material pieces to be welded) that are mounted and stacked one on the other on a stage and a rotary tool rotating at high speed is pressed into the works. When a pin attached at a tip end of the rotary tool reaches the upper work, a portion of the upper work becomes heated and softened due to a friction with the pin of the rotary tool. As the portion of the upper work becomes softened, the pin of the tool is gradually inserted into and then through the upper work, and eventually reaches the lower work, when an interfacing portion between the works and the pin of the rotary tool as well as in the vicinity thereof is further heated and plastic flow occurs, whereby the upper and lower works are welded.
However, in such a prior art as mentioned above, when the works are welded at edge portions thereof, a defective joint may occur if a distance between the rotary tool and end faces of the works are too small. Specifically, as shown in FIG. 5, when a rotary tool 100 welds the works 110 at the edge portions 111 thereof, a softened part of the works that is stirred and soften may be squeezed out between the edge portions 111 of the works 110 due to an inner pressure that occurs during welding the works 110. This may cause a deformation such as a leaked overlay 112 (burr) between the works 110, 110, due to which the edge portion 111 of the upper work 110 warps, so that a gap 113 is generated between the edge portions 111, 111, resulting in a defective joint. Consequently, there have been difficulties in welding the works 110 at the edge portions 111, 111 thereof in a proper quality.
Therefore, it would be desirable to provide a friction stir welder and a method for friction stir welding for welding works at edge portions thereof in a high quality.